Explainer: The Zika Virus in Latin America

The Zika virus has appeared in 23 countries and territories in the Americas. Here's how governments are responding.

There's no known cure or vaccine for the Zika virus, but Brazilian researchers are on the case to find one.

Updated February 1—A mosquito-borne disease previously unseen in the Americas is now present in 20 Latin American and Caribbean countries and territories, prompting action from governments across the region and a travel advisory from the U.S. Centers for Disease Control and Prevention. While the disease only causes symptoms in 23 percent of those infected, scientists believe it may cause birth defects when pregnant women catch it and may be linked to a condition causing paralysis. Given that Brazil is experiencing more cases than anywhere else in the Americas, observers fear Brazil’s Carnival and the Rio Olympics this summer could lead to Zika outbreaks on a global level.

First identified in monkeys in the 1940s in Uganda’s Zika Forest, the virus spread through the Aedes aegypti mosquito species to humans in subsequent decades, becoming common in Africa and Southeast Asia. Related to dengue, yellow fever, and the West Nile virus, the disease causes mild effects like fever, red eyes, rash, and joint pain, though only one in five people infected develop symptoms. There is no vaccine or known cure.

The disease first emerged in May, and by October medical professionals saw a jump in cases of microcephaly. They made the connection between Zika and microcephaly, which can be also caused by other factors including alcohol and rubella. Through the end of 2015, an estimated 1.5 million people in Brazil contracted the disease, while doctors found close to 4,000 suspected cases of microcephaly from late October through mid-January—a more than 2,400 percent increase from the usual 150 cases per year. Brazil also identified a possible connection with Guillain-Barré syndrome after doctors diagnosed close to 300 cases of the rare condition in northern states last year.

Locally transmitted cases have been reported in at least 23 countries and territories in the Americas, including Barbados, Bolivia, Brazil, Colombia, Dominican Republic, Ecuador, El Salvador, French Guiana, Guadeloupe, Guatemala, Guyana, Haiti, Honduras, Martinique, Mexico, Nicaragua, Panama, Puerto Rico, Paraguay, Saint Martin, Suriname, the U.S. Virgin Islands, and Venezuela. The United States saw a number of cases, including a mother who gave birth to a baby with microcephaly, but patients had contracted the disease traveling abroad and, as of the time of this report, there had not yet been reported cases of local transmission.

The World Health Organization cautioned this week that, given the widespread presence of the Aedes mosquito, the disease could spread to every country in the Americas except Canada and Chile.

In Venezuela, the health minister said on January 29 that there are 4,500 suspected Zika cases in the country and 90 cases of Guillain-Barré, though she said there were no known cases of microcephaly. She said the government would make a “national offensive” against the disease-carrying mosquito. However, the government has been tight-lipped on Zika and, in contrast to other Latin American countries, was late to publicly discuss the outbreak. The health ministry hasn’t divulged a monthly report on communicable diseases since 2014. The Venezuelan Society for Public Health believes that more than 400,000 Venezuelans contracted Zika since July.

In reaction to the warning, Brazil Health Minister Marcelo Castro said he believed pregnant women can still safely travel by taking precautions against mosquito bites. But scientists predict Zika will spread globally, and one researcher told The New York Times the 2016 Rio Olympics could become a catalyst—especially since Zika may have been brought to Brazil during the World Cup. Experts also believe Brazil’s Carnival could be an “explosive cocktail” to spread Zika, given the number of foreigners and revelers in close contact, reports BBC Brasil.